(a) Field of the Invention
The present invention relates to a method for fabricating a core circuit board having passive components, such as resistors, capacitors and inductors, which can be used to construct a multilayer circuit board with embedded passive components.
(b) Description of the Prior Art
With an increasing tendency towards high performance and compact size, a circuit board is required to have a high degree of lamination and high density of circuitry. In order further to minimize the space requirements on circuit boards, implementation of the embedded passive components, such as resistors, capacitors, and inductors, in a multiplayer circuit have been developed.
Integrating a variety of passive components in a multiplayer circuit board can be accomplished in a number of ways. For instance, for thick-film resistor materials, such as a dispersion of silver powder or carbon particles in a resin or a dispersion of RuO2 and glass powders in a binder, the thick-film resistors can be made by the screen printing or roller coating method. In contrast, for thin-film resistor materials, such as Ni—Cr, Ni—P, Ni—Sn, Cr—Si, and TaN alloys, etc., the thin-film resistors can be formed by the sputtering, electroplating or electroless plating method. The selection of thick-film resistors or thin-film resistors to be used in making a multilayer circuit board is a trade-off of cost and fine component resolution.
A number of thick-film or thin-film materials for making passive components are well recognized. Currently, the critical issue is how to integrate the existing thick-film or thin-film passive components into the circuit board, which must be easily adaptable to the manufacturing process of a multilayer circuit board. Most of the methods in this field, such as those provided by U.S. Pat. Nos. 3,857,683, 5,243,320, and 5,683,928, made the thick film or the thin film passive components on the surface of the insulating layer by the screen printing and/or photoresist-etching method before stacking a new circuit layer in the process of manufacturing a multilayer circuit board. In the present time, however, only two types of embedded passives are commercially available for industrial mass production. One type is electroplated planar resistive material which is disclosed in U.S. Pat. No. 5,243,320. The other type is internal capacitive laminate which is disclosed is U.S. Pat. No. 5,870,274. However, the embedded capacitors and resistors attached to the same circuit layer have never been achieved in the prior art, which can be accomplished by the method proposed herein of combining the advantages of the fabrication processes which have been taught in the U.S. Pat. Nos. 5,343,320 and 5,870,274.
Accordingly, it is desirable to provide a method for fabricating the embedded capacitors and resistors attached to the same circuit layer in a multilayer circuit board, which is very preferable for achieving a high density multilayer circuit board.